During the manual or automatic application of lacquers to objects, a partial flow of the lacquer, which generally contains both solids and/or binding agents and solvents, is not applied to the object. In professional circles, this partial flow is called “overspray”. Furthermore, the terms overspray or overspray particles are always understood in the sense of a disperse system, such as an emulsion or suspension or a combination thereof. The overspray is gathered by the airflow in the spray booth and fed to a separator so that the air, possibly after a suitable conditioning, can be directed back into the coating booth again.
Particularly in plants with greater lacquer consumption, for example in plants for lacquering vehicle bodies, wet separation systems are preferably used in a known manner on the one hand or electrostatically operating dry separators are used on the other hand.
As alternatives to current, stationary wet and dry separation systems, which can also operate electrostatically, systems with exchangeable disposable separation units are also used, which systems after reaching a limit loading with overspray are exchanged for unladen separation units and disposed of or possibly recycled. The preparation and/or disposal of such separation units can be energetically more acceptable, and also more acceptable with regard to the required resources, than the cost in the case of a wet separator or an electrostatically operating separating device.
Overspray as a rule has strongly adhering properties and in most cases has liquid constituents, which makes the deposition and separation of the overspray from the exhaust air more difficult. For this reason, a filtration aid material, which facilitates a separation of the overspray, is fed to the overspray-laden exhaust air. The overspray particles are as a rule comparatively small and have a low mass. This additionally makes the separation more difficult.
For this, there are various known approaches. In this respect, DE 20 2014 001 981 U1, for example, describes ice being fed as filtration aid material. The overspray particles are bonded to the now, however, frozen liquid, like in the case of wet separation, as a result of which the mass and the volume of the particles present in the airflow are increased and their separation in for example a cyclone or other filter is made easier. After separation, liquid water, which has to be separated in a comparatively costly manner from the overspray, exists again.
A dry separation system, in which filtration aid material in the form of rock meal is fed to the overspray-laden exhaust air, is known from DE 10 2005 013 708 A1. This is deposited as a barrier layer on the filter surface and thereby prevents adhesion and blocking of the filter in use. The rock meal subsequently has to be separated as such from the overspray or disposed of partially still wetted with overspray, which can be problematic especially from the environmental engineering point of view.
A further dry separation system is known from DE 10 2011 117 667 A1. Separation units, which are designed as above-mentioned disposable separation units and after reaching a limit loading with overspray are exchanged as a laden disposable separation unit for an empty disposable separation unit, are provided there. An effective separation is also desirable here, however. Nevertheless, a filtration aid material in this case would to a considerable extent contribute to the limit loading of the disposable separation units, as a result of which the overall absorption of overspray per disposable separation unit would be reduced.